Disc screens have long been used to separate particulate materials such as wood chips into difference fractions, according to size. More recently, disc screens have been used to separate or classify mixed recyclable materials into respective streams of similar materials such as broken glass, containers, mixed paper and newspaper.
A disc screen typically includes a frame in which a plurality of rotatable shafts, or rotors, are mounted in a parallel relationship. A plurality of discs are mounted on each shaft and a connected drive rotates the shafts in the same direction. The discs on one shaft interleave with the discs on each adjacent shaft to form screen openings between the peripheral edges of the discs. The size of the openings determines the dimension (and thus the type) of material that will fall through the screen. Rotation of the discs, which have an irregular outer contour, agitates the mixed recyclable materials to enhance classification. The rotating discs also propel across the screen the larger articles which are too big to fall between the discs. The general flow direction extends from an input area where the stream of material pours onto the disc screen to an output where the larger articles pour off of the disc screen. The smaller articles fall between the discs onto another disc screen or a conveyor, or into a collection bin. One such disc screen is disclosed in U.S. application Ser. No. 14/797,090 filed on Jul. 11, 2015, assigned to the same assignee as this application. The contents of this patent application are incorporated herein by reference.
The discs of a disc screen normally have a central opening or bore that allows them to be slid over the end of a shaft which may have a round or square cross-section. See for example U.S. Pat. No. 4,836,388 of Bielagus, granted Jun. 6, 1989. Over time, the discs wear out and must be replaced. It is not practical to re-surface or repair damaged or worn discs without removing them from the shafts of the disc screen. However, it is tedious to dismount the ends of the shafts of a disc screen from their respective bearings so that the old discs can be removed and replaced by sliding the discs off the ends of the shafts. Moreover, if only single disc is worn out or broken, it is usually necessary to remove several discs before the damaged or broken disc can be slid off the shaft. In order to alleviate these problems, a split disc was developed by CP Manufacturing, Inc. of National City, Calif. See U.S. Pat. No. 6,318,560 of Robert M. Davis, granted Nov. 20, 2001. The split disc is comprised of two identical halves which are assembled around a shaft and tightly held together by a pair of bolt assemblies which clamp the disc to the shaft. Each disc half is made of an outer rubber portion which is stiffened with a rigid internal metal frame embedded inside the rubber portion.
While the split disc design is beneficial in removing particular discs without disturbing other discs on the shaft, typical disc screens may employ 600 or more discs. With so many discs, the process of replacing one disc at a time may still be too time-consuming. In order to alleviate these problems, multi-disc assemblies have been developed as demonstrated in U.S. Pat. No. 7,261,209 to Duncan, et al. The multi-disc assemblies comprise multiple discs that can be replaced at the same time, reducing the amount of effort in servicing a disc screen. However, the multi-disc assembly of Duncan involves a complex mounting arrangement involving a securing hub and mounting plate between the multi-disc assembly and the shaft.
A multi-disc assembly that is even more convenient to remove and install is described in U.S. Pat. Nos. 8,517,181 and 9,027,762, assigned to the same assignee as this application. The contents of these patents are incorporated herein by reference.
In disc screen systems, wrapping occurs when an object can fit through the interface opening of a screen. Therefore, it is advantageous to remove the opening from a disc screen if the disc screen is not being used for size separation. When the opening is removed, it becomes difficult to change discs on a screen because there is no way to reach through the screen to hold the disc in place when attaching a new disc. This leads to decreased performance as discs are used beyond their normal wear life.
Current designs typically require two workers to replace a disc assembly. While one worker is underneath the disc screen, holding one half of a disc screen in place, a second worker mates the second half of the disc screen and permanently fastens the halves together. In some cases, the drives must be disconnected so the entire shaft can be removed using a crane, transported to a repair facility, then reinstalled after disc replacement. This is not only dangerous for the workers, but it is also inefficient. Thus, it would be desirable to provide a device and method for attaching a disc assembly to a shaft such that the disc assembly may be removed and installed by a single worker.